When providing health care, the use of bladder catheters is often required. Bladder catheters in use today are composed of a flexible catheter shaft, to whose distal end, which is placed in the urinary bladder, a fluid-refillable balloon element is fastened. The catheter shaft has a filling channel, which leads into the balloon interior via an opening in the catheter wall. The main purpose of the balloon element is to securely mechanically anchor the catheter in the urinary bladder. In addition, when placed in the opening of the bladder, the balloon has a certain sealing function and prevents urine from flowing out of the bladder, past the catheter and through the urethra.
In the unfilled state, the balloon element resembles a sleeve pulled over the catheter shaft, fitting on the shaft all-around, typically under slight tensioning, in any case, however, in a fold-free manner. The sleeve is comparable to a hose fitting, and is usually fabricated from the same material or a substantially identical material as the shaft, but is modified in its elongation properties. Conventional balloon elements are designed with this specific type of construction, which, in the emptied state, fits closely on the shaft, to enable the balloon element to be advanced with as little as possible resistance, through the urethra into the bladder lumen. In this way, painful irritations or lesions of the urethra's mucous membrane, caused by folds or bulges in the wall of the balloon element that previously existed or formed during the advancing motion, are avoided when inserting the catheter. Once the balloon element is securely introduced into the bladder, the sleeve (balloon element) closely fitting on the shaft, is elastically expanded into a balloon by a fluid, under relatively high pressure. The material typically selected for the catheter shaft and the balloon element of conventional catheters, latex or silicon, permits an elastic expansion of the balloon element to a volume of 5 and 30 ml, respectively. These are the two standard balloon volumes for bladder catheters used in clinical practice.
Ideally, the balloon element, that has been elastically expanded into a balloon, fully retracts, even after a longer-term use of the catheter, and closely fits on the catheter shaft as a sleeve-type hose fitting, without forming folds or bulges. In this way, the drained balloon element does not cause any painful irritation or trauma to the sensitive urethra epithelium even during removal of the catheter. Typically, however, the balloon element, that has been elastically expanded for an extended period of time into a balloon, is not able to be fully elastically retracted onto the shaft. The partial loss of the sleeve elasticity caused by an elastic expansion of the balloon element over several days can be accelerated by the action of chemically aggressive urinary components (e.g., uric acid). In the case of latex-based catheters, given a long-period use, the urine regularly leads to a pronounced stiffening of the balloon element, but also to a considerable loss of elasticity of the catheter shaft. Once drained, balloon elements of the known type of construction, having a latex- or silicon-based sleeve, often exhibit residual, coarse folds or bulges in the (not fully) retracting envelope, and pose a considerable risk of injury to the patient.
Moreover, catheter materials customarily used up to now (latex, silicon, or latex- or silicon-based materials, and/or composite materials made of latex and silicon) have other clinically relevant disadvantages.
One drawback (particularly when latex materials are used) is that the balloon element does not always open out symmetrically with respect to form when elastically expanding and can burst in response to slight lateral weighting. The stability of the balloon anchoring in the opening of the bladder can be adversely affected by a pronounced asymmetry of the balloon with respect to form. Moreover, a pronounced asymmetry of the filled balloon element, depending on its placement in the opening of the bladder, can cause the catheter lumen to snap off.
A further disadvantage is that the balloon element of catheters of a conventional type of construction, as necessitated by the particularities of the manufacturing and the material, must remain below specific wall thicknesses. The minimum wall thickness of the elastically expanding sleeve, when filled to form the balloon, must be such that it is able to avoid, with certainty, falling below a lower, critical minimum wall thickness, below which the danger of rupture exists, in response to increasing shaping-out of the balloon (and the reduction in the balloon wall thickness accompanying the elastic expansion). The minimum wall thickness of the balloon element that fits on the shaft in the manner of a sleeve is typically within the range of at least 100 micrometers and requires relatively high pressures when the sleeve undergoes elastic expansion or deformation. During expansion, the balloon element assumes a shape predominantly in the radial, but also in the longitudinal direction (elongation). With increasing filling volume, the pressures forming in response to the predominantly radial elastic expansion of the balloon envelope in many cases cause a compression or stenosis of the drainage lumen of the catheter. This lumen-narrowing effect is furthered by the likewise occurring elastic expansion of the balloon in the longitudinal direction and, as a consequence thereof, the elongation of the catheter shaft in the balloon region. Both elongation components can lead to a considerable narrowing or stenosis of the catheter lumen.
It is a complex process to manufacture conventional bladder catheters, and one that requires many individual steps. In many cases, the particular dipping or molding processes do not ensure a satisfactory surface quality of the catheter and balloon. Above all, the silicon processing yields slightly rough and irregular boundary surfaces. This promotes the incrustation of urinary components, as well as the bacterial colonization of catheter surfaces.
The particular difficulty also arises when silicon is used, of water substantially permeating through the balloon envelope. To ensure that the balloon is adequately filled, it must typically be refilled in an almost daily cycle.